Properties of iron-oxides from red soils derived from volcanic tuff in West Java

Abstract

The properties of iron oxide concentrates of Oxisols and Alfisols on volcanic tuff in West Java, Indonesia, were studied by XRD,TGA, TEM and chemical analysis.Goethite and hematite are the co-dominant iron oxides and are present in all samples. Iron content of the soils (dithionite-soluble Fe) ranges from 6.0 to 15.4%. Aluminium substitution in goethite and hematite ranges between 11 and 26 mol% and 0 and 9 mol% respectively. The Al substitution in hematite increases at about half the rate for goethite within the same samples. Crystal size of goethite and hematite was measured from line broadening of the 110 reflections and ranges between 7 and 18 nm for goethite with a mean value of 10 nm and between 7 and 28 nm for hematite with a mean value of 18 nm. The dehydroxylation temperature of goethite is in the range 290-320 °C and is linearly related to Al substitution by the equation y = 280 + 1.53x, (R(2) = 0.53). The goethite and hematite in these Indonesian soils are very similar to these minerals in tropical and Mediterranean soils from other regions.